This breaks down if there is less competition for labour, and we enter a new Depression era. Under your logic, capitalists will pay nearly nothing for labour because there is so much of it. Then "society" has to step in and not-so-gently point out that these are people we're talking about, and they need things like dignity, time off, good health, good working conditions, as well as money.

We have to remember that people are the point of the economy: the economy exists to provide for all the people, people don't exist to be economic assets. There is a tendency for capitalists to forget this, and then we have to prod them with pitchforks to remind them.